Hearts of Iron IV

Hearts of Iron IV, also commonly known as HOI4, is a 2016 grand strategy video game developed by Paradox Development Studio and published by Paradox Interactive. It is the sequel to 2009's Hearts of Iron III and the fourth main installment in the Hearts of Iron series. Like previous games in the series, Hearts of Iron IV is a grand strategy wargame that focuses on World War II. The player can control any country in the world, starting either in 1936 or 1939. Players have the option of following a nation's historical path, or leading various non-historical paths. The game allows players to take part in both single-player and multiplayer modes.

By May 2018, the game had sold a total of one and a half million copies worldwide. As of November 2025, the game has sold over seven million copies on Steam alone. Since its release, Paradox has released large amounts of downloadable content for Hearts of Iron IV.